CVE-2026-48768 Overview
CVE-2026-48768 affects TypeBot, an open-source chatbot builder tool. Versions 3.16.1 and earlier expose an unauthenticated endpoint at POST /api/blocks/file-input/v3/generate-upload-url that issues presigned S3 PUT URLs. The endpoint uses unsanitized fileName input to construct object keys and does not bind Content-Type on the presigned URL. Any anonymous visitor to a published bot containing a file input block can upload attacker-controlled HTML, SVG, or JavaScript content to arbitrary subpaths under the public/ prefix, including paths owned by other tenants. The flaw is classified under CWE-22 (Path Traversal) and is fixed in TypeBot 3.17.0.
Critical Impact
Unauthenticated attackers can upload arbitrary HTML, SVG, or JavaScript into the storage bucket and overwrite content on other tenants' published bot paths, enabling stored cross-site scripting on the storage origin.
Affected Products
- TypeBot versions 3.16.1 and earlier
- TypeBot deployments backed by S3 or MinIO object storage
- Multi-tenant TypeBot instances serving published bots from a shared public/ prefix
Discovery Timeline
- 2026-06-18 - CVE-2026-48768 published to NVD
- 2026-06-18 - Last updated in NVD database
- v3.17.0 - Patched release published on GitHub
Technical Details for CVE-2026-48768
Vulnerability Analysis
The vulnerability resides in the generate-upload-url API route used by TypeBot's file input block. The endpoint accepts a client-supplied fileName value and concatenates it into an S3 object key under the public/ prefix. The server then signs a PUT URL for that key and returns it to the caller. Two distinct weaknesses combine to produce the impact. First, the endpoint requires no authentication, so any visitor to a published bot can request signed upload URLs. Second, the presigned URL omits a Content-Type binding, allowing the uploader to set arbitrary MIME types such as text/html or image/svg+xml during the PUT. Files served from the storage origin can therefore execute script in a browser context.
Root Cause
The root cause is improper neutralization of path separators in the fileName parameter combined with missing authentication on the URL-generation endpoint. The server treats forward slashes inside fileName as legitimate key structure rather than rejecting or encoding them. S3 and MinIO canonicalization block ../ traversal because the canonical request used during signature validation no longer matches, producing a signature mismatch. Forward-slash injection is not normalized away, so an attacker can place objects at arbitrary keys such as public/<other-tenant-id>/results/<file>.
Attack Vector
An attacker locates any published TypeBot that contains a file input block. The attacker calls POST /api/blocks/file-input/v3/generate-upload-url with a crafted fileName containing forward slashes that target another tenant's result path or any chosen subpath under public/. The server returns a presigned PUT URL. The attacker uploads HTML, SVG, or JavaScript content with an attacker-chosen Content-Type. The hosted object is served from the storage origin and can execute script when a victim loads it, producing stored XSS scoped to the storage origin and enabling arbitrary content hosting on the platform.
No proof-of-concept exploit code is referenced in the advisory. See the GitHub Security Advisory GHSA-fp7x-6pqh-vhvf for full technical detail.
Detection Methods for CVE-2026-48768
Indicators of Compromise
- Requests to /api/blocks/file-input/v3/generate-upload-url with fileName values containing forward slashes, percent-encoded slashes, or path-like segments.
- S3 or MinIO objects under the public/ prefix with extensions such as .html, .svg, .js, or .xhtml that do not correspond to legitimate file-input submissions.
- Objects stored under one tenant's result path that were written by sessions originating from a different bot or tenant identifier.
- HTTP PUT requests to presigned URLs carrying Content-Type: text/html or image/svg+xml when the originating block is a file input.
Detection Strategies
- Parse application logs for generate-upload-url calls and alert on any fileName containing /, %2F, or \.
- Run periodic bucket inventory scans against the public/ prefix and flag objects whose MIME type is script-capable.
- Correlate upload session identifiers against the bot and tenant identifiers in the storage key to detect cross-tenant writes.
Monitoring Recommendations
- Forward TypeBot application logs and S3 or MinIO access logs to a centralized analytics platform for retention and query.
- Monitor for spikes in anonymous calls to the file-input upload endpoint from single source addresses.
- Track CDN and storage-origin responses for served text/html or image/svg+xml content under paths intended for user file uploads.
How to Mitigate CVE-2026-48768
Immediate Actions Required
- Upgrade TypeBot to version 3.17.0 or later on all self-hosted and managed deployments.
- Audit the public/ prefix in the backing S3 or MinIO bucket and remove any objects with script-capable MIME types that were not produced by legitimate uploads.
- Rotate any session tokens or API credentials that may have been exposed through stored XSS on the storage origin.
- Review CDN and reverse-proxy configurations to ensure the storage origin is served from a sandboxed domain separate from authenticated application surfaces.
Patch Information
The fix ships in TypeBot 3.17.0. Release notes are published at the TypeBot v3.17.0 release page. Coordinated disclosure details are available in GitHub Security Advisory GHSA-fp7x-6pqh-vhvf. The patched release validates fileName input, restricts presigned URLs to expected content types, and constrains object keys to the calling session's scope.
Workarounds
- If immediate upgrade is not possible, place an authenticating reverse proxy or WAF rule in front of /api/blocks/file-input/v3/generate-upload-url to reject fileName parameters that contain /, \, or %2F.
- Configure the storage bucket policy to deny PUT operations that set Content-Type to text/html, application/xhtml+xml, image/svg+xml, or application/javascript.
- Serve the public/ prefix through a CDN that forces Content-Disposition: attachment and a non-executing MIME type for user-uploaded objects.
- Isolate the storage origin on a dedicated domain that holds no application cookies or tokens to limit the impact of stored XSS.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
